Cambrian fossil pushes back evolution of complex brains

This picture shows a nearly intact fossil of Fuxianhuia protensa. The inset shows the fossilized brain in the head of another specimen.

The remarkably well-preserved fossil of an extinct arthropod shows that anatomically complex brains evolved earlier than previously thought and have changed little over the course of evolution. According to University of Arizona neurobiologist Nicholas Strausfeld, who co-authored the study describing the specimen, the fossil is the earliest known to show a brain.

The discovery will be published in the Oct. 11 issue of the journal Nature.

Embedded in mudstones deposited during the Cambrian period 520 million years ago in what today is the Yunnan Province in China, the approximately 3-inch-long fossil, which belongs to the species Fuxianhuia protensa, represents an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan.

The fossil provides a "missing link" that sheds light on the evolutionary history of arthropods, the taxonomic group that comprises crustaceans, arachnids and insects.

The researchers call their find "a transformative discovery" that could resolve a long-standing debate about how and when complex brains evolved.

"No one expected such an advanced brain would have evolved so early in the history of multicellular animals," said Strausfeld, a Regents Professor in the UA department of neuroscience.

According to Strausfeld, paleontologists and evolutionary biologists have yet to agree on exactly how arthropods evolved, especially on what the common ancestor looked like that gave rise to insects.

"There has been a very long debate about the origin of insects," Strausfeld said, adding that until now, scientists have favored one of two scenarios.

Some believe that insects evolved from the an ancestor that gave rise to the malacostracans, a group of crustaceans that include crabs and shrimp, while others point to a lineage of less commonly known crustaceans called branchiopods, which include, for example, brine shrimp.

Because the brain anatomy of branchiopods is much simpler than that of malacostracans, they have been regarded as the more likely ancestors of the arthropod lineage that would give rise to insects.

I don't think anyone is suggesting that this arthropod is the ancestor of modern complex-brained animals - but the fact that this fossil shows evidence of a brain much larger and more complex than was previously believed to exist that far back suggests that large complex brains first showed up even earlier, and maybe when vertebrates and invertebrates split they were already "brainier" than we ever imagined.

Or alternately, perhaps large complex brains evolved multiple times independently. That would imply that there may have been other ancient species with large brains that we have not found fossils of yet, maybe many intelligent lineages we know nothing about.

Either way, we have just learned that the world is different than we thought, weirder than we thought, and that is always a cool thing. That is our big advantage over the religious - finding out that what we believed was wrong is icing on the cake for us, while it is spoilage for them, mildew on the cake instead. What disturbs and depresses them excites us.

Sean, the brain is an amazing organ. During my training, I had to learn how to teach and the way we learned was to teach different animals with brains how to do something we wanted them to learn. I taught rats, pigeons, dogs, fish and octopus how to do something. That is the function of the brain is to change behaviors by learning different ones. We would know we were successful if the organism changed its normal behavior. For example, we changed access to food by teaching the organism to push a lever. Learning means change in behavior. We teach our children how to behave at home and in public, teachers teach children how to read and write and a lot of other things. These are things that do not come naturally to even human children. We "socialize" them. Unless there is a brain dysfunction, we train our children how to whine, misbehave at restaurants and grocery stores. With a little coaching, a parent can learn how to teach their children socially appropriate behaviors. Children have many influences on them and they learn from peers, videos and a lot of other ways. It is not only parents, but as to healthy discipline, parents and teachers have a great influence on what they learn and retain.